The invention relates to a strand feeding device with a storage drum and a strand guide element arranged in the region of the lower edge of the storage drum and being adjustable into a first position for intermittent strand feed and a second position for positive strand feed.
In devices using or consuming strands, e.g. textile machines, especially knitting machines, it is frequently desired to feed thread, strand, strip or wire type material or the like, referred to briefly as strands, selectively continuously or intermittently (DE-PS 2 939 803, U.S. Pat. Nos. 3,418,831, 4,027,505). Strand feed devices used primarily for this are so-called belt feeders, which have a rotatable strand drum with a first peripheral section in contact with a feed and transport conveyor formed as a belt and a second peripheral section free from the feed and transport conveyor. Accordingly, if the strand is between the first peripheral section and the feed belt, it is necessarily and continuously fed with a speed corresponding to the peripheral velocity of the strand drum or the transport velocity of the feed band (positive strand feed). If, however, the strand is arranged on the second peripheral section, it is only fed when a pull is exerted thereon by the device processing the strand (intermittent strand feed). To select the desired kind of feed, a strand guide element adjustable manually or automatically, especially under pattern control, is associated with the strand and can be coupled to a mechanical or electromagnetic control device and locates the strand on the first or the second peripheral section. Band feeders of this kind however involve two different disadvantages, which are unacceptable, especially in their use in knitting machines.
The first disadvantage consists in that the strand is drawn directly off a supply reel or the like during intermittent feed and can therefore only be fed with a comparatively high minimum tension. This is dependent on the one hand on the number of deflecting points between the strand feed device and the supply reel and on the other hand on the unavoidable fluctuations in tension imposed by the use of the supply reel and is determined more or less arbitrarily. Since no active feed device is provided in intermittent strand feed, unavoidable fluctuations in tension arise in this feed mode.
The second disadvantage consists in that, reliable changeover from positive to intermittent strand feed and vice versa presumes that the feed belt and the strand are in contact only over a small part of the circumference of the peripheral surface of the strand drum. Accordingly, it is hardly possible to effect the positive strand feed without some slip between the strand drum and the feed belt, so that differing strand tensions are unavoidable even in positive strand feed.
The two disadvantages last referred to do not occur in strand feed devices of the kind initially specified, so-called storage feeders. In fact known strand feed devices of this kind (DE-PS 1 760 600 or DE-PS 2 312 267) also have a strand guide element serving the purpose of selectively winding the strand off the storage drum tangentially with a speed corresponding precisely to the winding on speed (positive strand feed) or drawing the strand over the lower edge of the storage drum, substantially axially, i.e. overhead, with a speed dependent on the strand usage in the device (intermittent strand feed) In such strand feed devices the strand guide element can only be moved manually into the one or the other position, since it is not intended to bring the strand selectively into the one or the other position during running of the device using the strand, but is for setting the strand feed device either to permanent positive or permanent intermittent strand feed. In addition such storage feeders can be switched temporarily to intermittent strand feed if it is normally operating with positive strand feed, as is frequently desired during adjustment and repair work on knitting machines while substantially stationary or driven in creep mode.
The switching circuits or the like of the present invention are generally known in the art, for example in FIG. 1 to 4, of German offenlegungsschrift 23 13 274 which correspond to Great Britain patent 14 55 922 published on November 17, 1976. In FIGS. 2a to 4 there are disclosed four different switching circuits with respect to FIG. 1a, switch 11 is mechanically coupled with control element 9 in such a manner that if control element 9 is in the position shown in FIG. 1, the switch is in the position II. If the control element 9s is retracted, switch 11 is in position I. In switch position II, positive feed takes place, and in position II, intermittent feed takes place. Switch 11 is automatically controlled if the control element 9 is switched from one position to its other position. The same can be done in accordance with this invention, e.g. by means of the guide element 31 which can be compared with the control element 9 of the state of the art. The result of operating switch 11 of Offenlegungsschrift 23 13 274 is the same as disclosed in this application, i.e. a change between positive and intermittent speed.